This invention relates to a copolymer, and more particularly to a surgical article manufactured from the copolymer and to a method of manufacturing and using the surgical article.
Absorbable synthetic polymer sutures known in the prior art are usually manufactured, sold, and used as braids. The known absorbable polymers containing a glycolic acid ester linkage seem to be well suited for use as such braided sutures. However, some of them tend to form relatively stiff monofilaments, particularly in the larger diameters. Yet, some surgeons prefer the suturing characteristics of a smooth, continuous-surfaced monofilament suture. Thus, it has been recognized for some years that there is a need in surgery for flexible, absorbable, monofilament sutures which retain a safe and useful proportion of their strength for a relatively long period of time in vivo.
To be fully useful as an absorbable suture it is essential that a monofilament not only be absorbable and flexible but it must also be capable of a relatively long period of in vivo strength retention. An appropriate strength retention target for this type monofilament suture is considered to be about 35-42 days in vivo.
U.S. Pat. No. 4,243,775, Rosensaft and Webb, assigned to the assignee of the present invention, discloses a polymer material useful for forming both an absorbable braided suture and, under certain conditions, a flexible monofilament suture with extended strength retention. That patent discloses the sequential addition of a cyclic ester monomer, such as a lactide, lactone, oxalate or carbonate, to glycolide monomer in the copolymerization process using a monofunctional alcohol as an initiator. Disclosed are triblock copolymers with poly(lactide) units predominantly on both ends of a glycolide polymer chain, copolymers of trimethylene carbonate (1,3-dioxan-2-one) and glycolide, and monofilament sutures made therefrom.
In the glycolide-trimethylene carbonate copolymer monofilament of U.S. Pat. No. 4,243,775, flexibility and extended strength retention are obtained at high incorporation of the 1,3-dioxan-2-one. The disclosed triblock copolymer comprises poly(lactide) units as the end blocks and poly(glycolide) units as the middle block and is formed using a monofunctional alcohol.
The present invention provides a glycolide-trimethylene carbonate triblock copolymer that results in a monofilament suture which has an increased abosorption rate compared to the glycolide-trimethylene carbonate copolymer suture of U.S. Pat. No. 4,243,775. The present invention also provides a method of producing the desired copolymer which is easier to carry out than the polymerization process disclosed in that patent.